Stud fastening assembly

ABSTRACT

A stud fastening assembly 10 including a stud 11 having a threaded end threadable into a hole 15 formed in a workpiece 16 and a plurality of serrated rings 21 and 22 for securing the stud in place. The serrated rings include inner serrations 20 sized to slidably engage longitudinal serrations 14 formed on a mid-section of the stud and further include outer serrations 19 configured to engage the sidewalls of the hole formed in the workpiece and thereby prevent relative rotation. The lower ring includes fewer outer serrations than does the upper ring, to facilitate installation.

BACKGROUND OF THE INVENTION

This invention relates generally to stud fasteners, and, moreparticularly, to a stud fastening assembly secured to a workpiece by aserrated ring.

A typical example of a stud fastening assembly of this kind isillustrated in Japanese Patent Publication No. 43389/72. As shown inFIGS. 7, 8(a) and 8(b), a stud fastening assembly 10 includes a mainbody or stud 11 provided with male threads 12 and 13. The main body isthreadably inserted into a machined hole 15 of a workpiece 16 andfurther threadably engaged with an internal thread 17. The main body 11is provided with a longitudinal serration 14 located between theinnermost incomplete screw threads 12a and 13a of external threads 12and 13.

A fastening ring 18 is provided with an outer serration 19 and an innerserration 20. The inner serration 20 is slidably engaged with thelongitudinal serration 14 of the main body 11.

The outer diameter of the external threads 12 and 13 of the main body 11are larger than the inner diameter of the inner serration 20 of thefastening ring 18. Even if a relative axial movement with respect to themain body 11 is applied to the fastening ring 18, this axial movement islimited under an engagement with either of the incomplete screw threads12a and 13a. Therefore, the fastening ring 18 forms an engagement memberwhich is integral with the main body, forming a stud fastening assembly.

When the main body 11 of the bolt is threadably inserted to the desireddepth in a workpiece 16, an axial force is applied to the uppermost partof the fastening ring 18 and the outer serration 19 is set in a hole15a, which is slightly smaller than the serration's outer diameter.Material of the workpiece positioned between the individual outerserrations 19 may apply a resistance force against a rotational movementof the fastening ring. Since a relative engagement between the innerserration 20 of the fastening ring 13 and the outer serration 14 of themain body 11 prohibits a rotational movement of the main body 11, nohelical movement of the main body 11 is produced, causing the studfastening assembly to be kept at its close integral engagement with theworkpiece 16.

The fastening ring 18 for the stud fastening assembly has an integralform carrying both the outer serration 19 and the inner serration 20,and its axial thickness is larger than its radial thickness. This causesits press machining and plastic work to be difficult, requiring either acutting work or a sintering formation of powder metal ceramics to beperformed. However, such a machining process has a low productivity, anda reduction in cost is difficult.

SUMMARY OF THE INVENTION

This invention is embodied in a stud fastening assembly having aplurality of overlapping rings, each of which has an inner serration andan outer serration. The plurality of rings are made such that the numberof teeth of the outer serration of the upper ring is larger than thenumber of teeth of the outer serration of the lower ring. With thisconfiguration, it is possible to make a press machining that enables amass production. Further, the plurality of rings function the same asthe single ring of the conventional type of integral assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view in section showing a stud fasteningassembly of the present invention, in which a stud is threadedly engagedin a workpiece, and three overlapped fastening rings having serrationsare shown at the left side and right side of the stud, for indicating acondition before and after they are displaced to their fasteningpositions in the workpiece.

FIG. 2 is a view showing the stud fastening assembly, with the fasteningrings being positioned around the stud, and with the fastening ringsbeing shown in section at the right side of the stud.

FIGS. 3(a) and (b) are a top plan view and a side elevational view,respectively, of one ring of the stud fastening assembly of the presentinvention.

FIGS. 4(a) and (b) are a top plan view and a side elevational view,respectively, of a second ring of the stud fastening assembly, to beapplied below the ring of FIGS. 3(a) and (b).

FIG. 5 is a cross-sectional view showing a condition in which thefastening ring of FIGS. 3(a) and (b) is displaced to a fasteningposition in the workpiece.

FIG. 6 is a cross-sectional view similar to FIG. 5 showing a conditionin which the fastening ring of FIGS. 4(a) and (b) is displaced to afastening position in the workpiece.

FIG. 7 is an elevational view in section showing a prior art assemblyfor stud fastening assembly, wherein a single fastening ring withserrations is shown at its left side and right side for a conditionbefore and after it is displaced to a fastening position in theworkpiece.

FIGS. 8(a) and (b) are a top plan view and a side elevational view,respectively, of the prior art fastening ring of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to FIGS. 1-6 of the drawings, there is shown a studfastening assembly 10 in accordance with the invention. The assemblyincludes an elongated stud 11 and upper and lower overlapping fasteningrings 21 and 22, respectively, having a combined thickness the same asthat of a conventional, one-piece ring (FIGS. 8(a) and (b)). As shown inFIG. 1, the lower fastening ring 22 is initially displaced from itsfastened position in a hole 15a of a workpiece 16. The fastened lowerring is also shown in FIG. 6.

The upper fastening ring 21 is then fastened as shown in FIG. 5. Since aserration 23 is already machined in the hole 15a of the workpiece 16 bythe lower fastening ring 22, an outer serration 19' of the ring 21 ismade only with a machining of a screw thread 25 of a phantom serration,shown in FIG. 6. The numbers of teeth of the conventional type of ring(FIGS. 8(a) and (b)) are the same as the number of teeth of the outerserrations (19 and 19') of the upper ring 21 (FIGS. 3(a) and (b)). Sincethe number of teeth of the outer serration 19" of the lower ring 22(FIGS. 4(a) and (b)) is 50% that of the conventional type ring, a loadfor displacing the ring to its fastened position is reduced by about50%. As shown in FIGS. 4(a) and (b), even if the number of teeth isreduced by about 50% from that of the conventional type ring, no problemmay occur under the following consideration and rather the product mayeasily be installed.

When a load is applied to the stud fastening assembly, if the number ofteeth of the serrations 14 of the stud 11 bolt is the same as that ofthe outer serration, such a load as above applied to the outer serrationis low due to a larger circumference and radius than that of the stud.Therefore, a rate in which the loads applied to the serration of themain body of the stud bolt and the outer serration become equal iscalculated for a trial.

In reference to FIG. 5, each of the sizes in the serration of the mainbody of the stud bolt and the outer serration is defined as follows:

    ______________________________________                                         ##STR1##                    r.sub.1                                           ##STR2##                    r.sub.3                                           ##STR3##                    r.sub.2                                          Virtual radius of s --erration of                                                                        r.sub.4                                            stud (of)                                                                     Internal angle of outer serration (∠aeb)                                                           β.sub.1                                       Angle of thread at stud serrations                                                                       β.sub.2                                       (∠cfd)                                                                  Shearing angle of one tooth of an outer                                                                  α.sub.1                                      serration (∠aob)                                                        ______________________________________                                    

Shearing angle of one tooth of a stud serration: α₂ (∠cod) ##EQU1##

A ratio of a sectional area of each of the serrations to which ashearing force is applied is expressed as ab:cd.

Taking into account a rate in which a torque is applied, the followingequations can be expressed:

    T=f.sub.1 ×r.sub.1                                   (7)

    T=f.sub.2 ×r.sub.2                                   (8)

Therefore: ##EQU2## and f₁ :f₂ becomes ##EQU3## where A torque appliedto one thread of the stud: T

A force applied to one thread of the stud: f₂

Force applied to one thread of an outer serration: f₁

Inner radius of an inner serration: r₂

Radius of the workpiece hole: r₁

Since this means that a shearing force is inversely proportional toradius, assuming a rate of sectional area described above, a ratio ofshearing force per unit area, where each of the threads of theserrations may receive, can be expressed as: ##EQU4##

Calculation of terms for M8 is as follows: ##EQU5##

Replacing these numerical values with a term of ##EQU6## results in thefollowing equation: ##EQU7##

That is, since a shearing force per unit area applied to an outerserration corresponds to 56.9% of that of the serration of the bolt, ifthe number of threads of the outer serration corresponds to 56.9% ofthat of the serration of the stud, i.e. that of the inner serration, itmay equal the load applied to the inner serration. Therefore, if thenumber of threads of the outer serration is more than 56.9%, no problemmay be generated. Thus, if the fastening ring is made such that threerings are overlapped to each other as shown in FIG. 1, wherein one lowerfastening ring 21 and two fastening upper rings 22 are applied, the rateis 100% due to the fact that the number of threads of the lowerfastening ring 21 is the same as that of the inner serration. The numberof threads of the upper fastening ring 22 can be 100+50+50=200, if it is50% of that of the inner serration. Considering its rate with threerings being corresponded to 300%, the value may become200--300×100=66.7%, since this value is larger than 56.9%, no problemmay occur in view of its mechanical strength.

As shown in FIG. 6, when the lower fastening ring 22 is fixed in thehole 15a of the workpiece 16 and the upper fastening ring 21 isoverlapped on the former ring as shown in FIG. 5, the serration 19' isfixed to the thread 25 of the virtual serration of the hole and thefunction of the fastening ring is achieved.

In view of the foregoing description, it should be appreciated that thefastening ring of present invention is made to have an overlapped platetype ring to enable a press machining operation to be performed, to makeits mass production a stable quality and to provide a reduction in itscost, while providing the same function as that of the conventionaltype, integral ring.

Although the present invention has been described in detail withreference to the preferred embodiment, it is apparent that the preferredembodiment is a mere illustrative example and various modifications canbe applied thereto without departing from the principle of the presentinvention.

I claim:
 1. A stud fastening assembly comprising:a stud having a endsection adapted to threadedly engage a threaded hole in a workpiece andfurther having a central section with longitudinal serrations; and lowerand upper fastening rings, each ring having inner serrationscomplementary to the longitudinal serrations of the stud and outerserrations configured to engage the threaded hole in the workpiece,wherein the lower and upper fastening rings are positioned to encirclethe stud, and wherein the lower ring includes fewer outer serrationsthan does the upper ring.
 2. A stud fastening assembly as defined inclaim 1, wherein the lower fastening ring includes about one-half thenumber of outer serrations of the upper ring.
 3. A stud fasteningassembly as defined in claim 1, wherein each of the fastening rings hasan axial thickness less than the its radial thickness.
 4. A studfastening assembly as defined in claim 1, and further including anintermediate fastening ring having inner serrations complementary to thelongitudinal serrations of the stud and outer serrations configured toengage the threaded hole in the workpiece, wherein the intermediate ringis positioned to encircle the stud, between the lower and upper rings,and wherein the outer serrations of the intermediate ring correspond innumber to the outer serrations of the upper ring.